Mechanism for the gas-phase hydrogen fluoride-mediated decomposition of peroxyacetyl nitrate (PAN) studied by dft method

摘要

Density functional theory has been used to study the mechanism of the decomposition of peroxyacetyl nitrate (CH_3C(O)OONO_2) in hydrogen fluoride clusters containing one to three hydrogen fluoride molecules at the B3LYP/6-311 + +G(d,p) and B3LYP/6-311+G(3df,3pd) levels. The calculations clarify some of the uncertainties in the mechanism of PAN decomposition in the gas phase. The energy barrier decreases from 30.5 kcal mol~(-1) (single hydrogen fluoride) to essentially 18.5 kcal mol~(-1) when catalyzed by three hydrogen fluoride molecules. As the size of the hydrogen fluoride cluster is increased, PAN shows increasing ionization along the O-N bond, consistent with the proposed predissociation in which the electrophilicity of the nitrogen atom is enhanced. This reaction is found to proceed through an attack of a fluorine to the PAN nitrogen in concert with a proton transfer to a PAN oxygen. On the basis of our calculations, an alternative reaction mechanism for the decomposition of PAN is proposed.